1. Field of the Invention
The present invention relates to a process and to equipment for filtration of liquids. More specifically, this invention relates to a new and improved method and device for the filtration of a suspension and the back flushing of filter elements.
2. Description of Related Art
A process for filtration of a green liquor suspension by means of filtering in a pressure filter has previously been disclosed in SE-B-443,815. The process involves the suspension being introduced into the lower part of a pressure vessel which contains a number of filter elements hanging down together from a partition wall. During the filtration stage, filtrate flows through these filter elements and is conveyed away from the upper part of the pressure vessel above the said wall. Sludge collected on the surface of the filter elements is released intermittently by means of so-called counter current washing. After the washing, and after the liquid, including accumulated sludge, has subsequently been pumped away, the process is repeated.
A process and a device for filtering suspensions has previously been disclosed in SE-A-8903267-6. In this case, a pressure filter is utilized which has vertically arranged filter elements. During the regeneration process, the deposited material is first dried and back-flushing is then carried out in order to remove this material from the filter cloth. The pressure vessel was drained of unfiltered suspension prior to the regeneration phase.
In both these processes, the back-flushing is carried out by the filter elements being supplied with the back-flushing medium from above. Medium which is present in the filter elements and which is not utilized for the back-flushing itself is allowed to dilute the filtrate and/or the secondary suspension containing the sludge.
Another proposal has been, in the case of a pressure filter which has been marketed under the name "Cricket filter" by the company Ama Filter, to initiate the back-flushing of flat filter elements, which hang down from an upper structure, from the area of their lower part in order thereby to improve the characteristics associated with the back-flushing. However, the back-flushing liquid is supplied from above and the liquid present in the filter element has no possibility of self-draining.